Author newsletters have always seemed to me like SPAM. Couldn't imagine why anyone would want to receive one.
However Chris Barton makes an excellent case for them in a guest post at Cynsations. What made me take notice was his point about Facebook updates and blog posts being too much for some readers. I think it's very possible that readers are overwhelmed by them, deadened by all the words. So, yeah, maybe a good, professional, occasional newsletter would be more of more benefit to everyone.